The present invention relates to a cutting insert for application in rotary end mills for the machining of metallic workpieces. In particular, the invention relates to a cutting insert formed of sintered powder and having a center hole for receiving a fastener.
Milling inserts for end mills are generally manufactured through form-pressing and sintering of a cutting material-forming powder. Such inserts typically possess positive cutting edges having positive rake angles since these inserts have showed the ability to reduce the cutting forces and the power supply needed in a tooling machine while at the same time diminishing undesirable vibrations. It is often desirable to provide the tool with a geometry having a positive axial angle and a negative radial angle. In certain cases a combination of positive axial angle and zero degree radial angle can be used in order to obtain a helical chip that provides the best chip transport. The cutting insert is usually clamped by a center locking screw which passes through a center hole of the insert.
In order to enable the insert to machine a 90-degree shoulder in a workpiece which is substantially straight, it has been proposed to make the main cutting edge of the insert wave-shaped e.g., as disclosed in U.S. Pat. Nos. 6,142,716; 6,193,446; and 6,196,770.
Also, it has been proposed in U.S. Pat. No. 5,365,805 that each side surface along which a main cutting edge is formed be provided with a recess. The recess divides at least a lower region of the respective side surface into two spaced-apart abutment surface segments which abut against a support surface of the insert-receiving site when the insert is installed in a holder. The patent recites that the length of the recess can be as much as 25-35% of the length of the associated side surface. That dimensioning results in the length of the recess being less than the diameter of a main cylindrical part of the center hole of the insert.
That fact is important for the following reason. During the manufacture of the insert, powder is inserted into a container having the general shape of the final insert and is then compressed and sintered. During the compression step, a portion of the powder is pressed against a center core which functions to form the center hole in the inset. That portion of the powder becomes more highly compressed than the remaining powder, whereupon during the sintering step, the more compressed powder shrinks to a lesser extent. As a result, the respective side surfaces of the insert assume a slightly convex shape which can interfere with the ability of the side surfaces to form a stable abutment with the support surface of the insert-receiving site of the holder.
In the case of the above-described short recesses disclosed in U.S. Pat. No. 5,365,805, some of the convexity of the support surface will remain notwithstanding the presence of the recess. Moreover, in the case of U.S. Pat. No. 6,142,716, the recess does not extend to the bottom of the insert, whereby a short-height section of the side surface remains, which due to its convexity, could present an obstacle to achieving a stable abutment, if contacting the support surface.
The present invention relates to an indexible cutting insert for chip forming machining. The insert comprises a basically parallelogram shaped body which is formed of sintered powder. The body includes a top face forming two main cutting edges. Each main cutting edge is convex as the insert is viewed in a direction perpendicular to the top surface. The body also includes a bottom face, and two longitudinal side surfaces extending downwardly relative to respective main cutting edges. The body also includes two end faces spaced apart in a longitudinal direction of the insert. Each end face has a bevel provided on a portion of the body protruding in the longitudinal direction from the remainder of the body. Each of the side surfaces has a height increasing toward a respective active cutting corner of the insert such that the active cutting corner is raised with respect to an opposite end of the respective side surface. The side surfaces are generally inclined at an acute angle toward the top face and at an obtuse angle toward the bottom face. An upper portion of each of the side surfaces comprises a wave shaped primary clearance surface extending along the entire respective main cutting edge at a downward inclination to form a clearance angle. A center hole extends completely through the body from the top face to the bottom face and includes a cylindrical portion adapted to receive a threaded shank of a clamp screw. The center hole further includes an enlarged portion disposed adjacent the top face. A lower region of each longitudinal side surface defines an abutment surface adapted to engage a support surface of an insert site of a holder. The lower region includes a recess extending to the bottom surface and extending in the longitudinal direction for a distance equal to at least 120% of a diameter of the cylindrical portion of the center hole (preferably at least 120% of that diameter), wherein the recess extends beyond the entire cylindrical portion in the longitudinal direction of the insert as the insert is viewed in a direction toward the side surfaces.
The invention also pertains to a mill tool comprising a holder and the above-described indexible cutting insert, wherein the recess extends beyond the entire cylindrical portion in the longitudinal direction of the insert as the insert is viewed in a direction toward the side surfaces.